Prostaglandin A1 metabolism and inhibition of cyclic AMP extrusion by avian erythrocytes.
1985; Elsevier BV; Volume: 260; Issue: 21 Linguagem: Inglês
10.1016/s0021-9258(17)39060-9
ISSN1083-351X
AutoresLynn E. Heasley, Laurence L. Brunton,
Tópico(s)Coccidia and coccidiosis research
ResumoTo probe the mechanism of this action of PGA,, we have studied the interaction of [3H]PGAI with suspensions of pigeon red cells.The interaction of PGAl with pigeon red cells is a multistep process of uptake, metabolism, and secretion.13H] PGA, rapidly enters red cells and is promptly metabolized (V,,, 5: 1 nmol/min/107 cells) to a compound(s) that remains in the aqueous layer after ethylacetate extraction.The glutathione-depleting agent, diamide, inhibits formation of the PGA, metabolite.In agreement with the order of potency of other prostaglandins to inhibit cAMP efflux (A >> E = B > F), PGA2 forms a polar adduct whereas prostaglandins E2, B,, and Fz, do not.The red cells secrete the polar metabolite of PGAl by a saturable mechanism (at 37 OC, K , = 0.6 &My V , , = 0.5 pmol/min/107 cells) that lowered temperatures inhibit (Eact = 21 kcal/mol).Because uptake and metabofism progress with much greater rates than metabolite secretion, red cells transiently concentrate the polar compound intracellularly.Onset and reversal of inhibition of cyclic AMP export by PGAl coincide with accumulation and secretion of PGAl metabolite, suggesting that the polar metabolite acts at an intracellular site to inhibit cyclic AMP efflux.In the aceompanying Appendix, we present chromatographic and amino acid analyses demonstrating that the polar metabolite is a glutathione adduct of PGAI.Intracellular cAMP escapes from many bacterial, acrasial, and metazoal cells, In avian erythrocytes and cultured mammalian cells, cAMP escapes by an energy-dependent mechanism that has many properties of active transport (1-3).One of the remarkable features of cAMP extrusion is its inhibition by certain prostaglandins (2, 3).We have characterized this inhibitory effect of prostaglandins in pigeon erythrocytes, a system in which PGAI' is the most potent inhibitor (2).The effect of PGAl is rapid, irreversible to washing, enhanced by lower temperatures, and unrelated to alterations of adenylate cyclase activity or cellular ATP.In addition, the order of potency of the prostaglandins as inhibitors of cAMP efflux
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